In vivo tissue extracellular volume fraction measurement by dynamic spin-lattice MRI relaxometry - Application to the characterization of muscle fiber types

RATIONALE AND OBJECTIVES. The extracellular volume fraction (v) was estimated in leg rabbit muscles by MRI dynamic longitudinal relaxation rate (R-1) relaxometry to distinguish between slow- acid fast-twitch muscle fiber types. METHOD. The extracellular volume fraction was calculated from the dynamic increase of the longitudinal relaxation rate after intravenous administration of a gadolinium (Gd-DTPA) contrast bolus, assuming a biexponential plasma concentration model. RESULTS, If has been shown that the extracellular volume fraction increases with the slow fiber content (oxidative type I); the maximal value (v = 0.186 +/- 0.018) was obtained in pure slow-twitch muscle fiber (100% type I). CONCLUSION. NMR extracellular volume estimates closely agree with those obtained using the more classic invasive isotopic method (Tc-99m-DTPA) carried out on the same rabbit strain and with data reported in the literature, The method has potential applications to characterize the pathophysiologic status of tissues. It is also applicable to a wide range of tissues and pathologies, in particular for the characterization of malignant tissues and their response to therapies.